Waterproofing is the combination of materials used to prevent water intrusion into the structural elements of a building or its finished spaces. Its main purpose is to resist hydrostatic pressure exerted by moisture in the liquid state. Waterproofing membranes consist of waterproof plastic, rubber, or coated-fabric materials. The materials are used in a system to prevent the ingress of water into foundations, roofs, walls, basements, buildings, and structures when properly installed. The term dampproofing is often confused with waterproofing, however, dampproofing is a system designed to resist the flow of moisture in a gaseous state i.e. water vapor.

Location of Waterproof Membrane

Depending on the structure and need, the waterproofing membrane can either be applied to the interior (negative), such as the case with repairs, the exterior (positive), or in places inaccessible by people (blindside).

Positive Side

Positive waterproofing membranes are applied to the exterior face of a structure. It can be applied above, below, or at grade to surfaces that will get wet due to exposure to weather conditions and the surrounding soil. Positive waterproofing is a critical step in construction because it prevents moisture infiltration and protects structural components, including the concrete and steel. It can also protect the surface from freeze-thaw cycles and corrosive chemicals. When used for below grade surfaces (such as sealing a foundation) it is available as a fluid applied membrane, sheet-membrane, or as hydros clay and vapor barriers. The disadvantage of positive side waterproofing is that it is inaccessible after construction except with costly removal of the topping landscape. Positive side waterproofing should be used alone when the surface will be exposed to corrosive soil, freeze-thaw cycles, and if there will be limitation to the interior humidity.

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Negative Side

Negative side waterproofing is applied to the interior face of a structure. It keeps water from entering an occupied space and is applied to what is known as the dry face. Negative side waterproofing is primarily used for water holding purposes (prevent water from entering space), but it does not prevent the water from entering the substrate (wall). The materials used for negative waterproofing must be able to withstand hydrostatic pressure. The most commonly used materials are epoxy injections and cementitious coatings. The advantage of negative side waterproofing is that it is accessible after installation for repairs or updates. Negative side waterproofing allows moisture into the substrate which can be seen as an advantage and disadvantage. Moisture promotes active curing of the concrete substrate, but it contributes to the corrosion of the concrete and steel reinforcements from the groundwater and chemicals. This type of membrane does not protect against the effects of the freeze-thaw cycle and can only be used on cemenitious systems.

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Blind Side

Blind side waterproofing is a difficult membrane to apply. It is used when the waterproofing can't be applied after the walls of the structure have been poured. Blindside waterproofing is applied before the concrete structure is poured, generally over the soil retention system. This system is best used for "zero lot line" foundation walls, tunnels, and any job site in a high-density, build-up area. Blindside is often also used for "green" projects because it minimizes the amount of site area that needs to be disturbed.

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In general, positive side waterproofing is the most effective form of new construction waterproofing. Using negative waterproofing increases the chance of ground containments or chemicals entering the substrate and deteriorating the concrete and corroding the steel reinforcements. The risk with using negative side waterproofing is that can get pushed out or dis-bonded from the substrate due to the moisture building up in the concrete. For negative waterproofing to be effective it must be mineral based like the substrate, penetrate into the substance to prevent being pushed off, and free from chloride that could harm the steel reinforcements.

Design Tip: The optimal solution for waterproofing during new construction is to apply positive side waterproofing and limit the negative side waterproofing to repairs and touch ups.

Above vs. Below Grade

Another important consideration when selecting a waterproofing membrane is whether the system will be above or below grade. Above grade applies to all of the structure that is above the ground level, while below grade refers to any portion of the structure that is located below the ground level. The waterproofing used in above grade systems will differ significantly from those used in below grade applications.

Above-grade waterproofing systems must meet several requirements. They must be breathable to prevent liquid from seeping into the space, but allow water vapor inside the wall to escape. Because the membrane will be exposed to light, it must be UV resistant. This is especially true for roofing systems. Above-grade waterproofing must be resistant to abrasion and corrosion because they are often used where there is a high volume of foot or vehicle traffic. This also means that they must be aesthetically pleasing. The term above grade applies to horizontal surfaces such as roofs, balconies, and parking docks, as well as vertical surfaces such as walls.

Below-grade waterproofing systems are a required step in building a structure. In order to be effective, below-grade waterproofing systems must be resistant to hydrostatic pressure and chemical erosion, be able to perform in high groundwater, have a low absorption rate, uniform thickness, and be flexible. The material used for below grade waterproofing is determined by the properties of the surrounding soil.

Types

The type of waterproofing membrane chosen dictates how the waterproofing material will be applied to the structure. Each type of material and structure has its own specific application requirements. It is important to understand how each system works and the proper application.

Applied or liquid membrane - Spray applied membranes, cold-fluid-applied membranes, and hot-applied membranes are types of membranes applied by melting and then fusing a rubber, bitumen, or elastomer layer onto the surface to be waterproofed. Liquid membranes have grown in popularity for horizontal applications. Polyurethane elastomers are the most common material composition for a fluid-applied elastomer membrane. However, bitumen and other epoxy-modified spray-applied membranes are also available. The temperature at the time of curing is very important because temperature-based applications are highly sensitive major temperature fluctuations which could cause the membrane to seal incorrectly. Liquid membranes are not removable or repositionable.

• Cold-fluid-applied membranes are brushed, rolled, or sprayed onto the surface to be protected. The liquid membrane dries or cures into a permanent waterproof membrane.
• Hot-applied systems should include a thermometer so the temperature can be monitored throughout the process. The temperature must be kept within 25 degrees of the required application temperature to ensure even application.

Film or sheet membrane - Sheet, self-adhering sheet, sheet metal membrane, and sheet metal waterproofing membranes fall into this category. Film or sheet membrane are attached to a surface using adhesives, mortar, tape, straps, anchors, plastic welding, or fasteners. Membrane sheets can consists of bentonite clay, modified bitumen, rubber, polyethylene, polypropylene, ethylenepropylenediene monomer (EPDM), reinforced polymers, and other rubber and plastic sheet compositions.

• Self-adhering membranes, also known as "peel and stick" membranes, have an integral layer of adhesives, so adhesives do not need to be applied to the surface of membrane at the work site. The release liner is peeled off the adhesive coating and the membrane stuck onto surface at the construction site.
• Some non-adhesive sheet membranes can be removed and repositioned. PVC sheet and polyurethane rubber sheets are common material compositions. The seams or joints between PVC thermoplasticwaterproofing sheets can be welded, which is an advantage over thermoset, urethane rubber-sheet membranes.

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Built-up or laminate membrane - Built-up waterproofing membranes can consist of thick viscosity tar, polymer mastics or cementious materials troweled or mopped onto a surface. Reinforcing layers of perforated felt, fiberglass, or fabrics are applied and then additional tar or mastics is layered onto the cloth reinforcement. 

Injectable waterproofing - Injectable waterproofing membranes are used in existing constructions requiring waterproofing improvements. Injectable waterproofing membranes are installed by drilling holes through a foundation's floors and walls and then pumping a liquid polyurethane, bentonite clay, or epoxy waterproofing compound behind the foundation wall or floor to form a positive side waterproofing membrane.

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Waterproofing Materials

Waterproofing membranes are made from several one or more layer materials such as rubber, elastomer, polyethylene, polypropylene, bitumen, polyvinyl chloride (PVC), polyurethanes, ethylene propylene diene monomer (M-class) rubber EPDM, silicate, bentonite clay, fabrics, fiberglass, cementious high-build coatings, composite layers, resin coatings, plastic sheeting, polymer liners, mastics and metal sheet.

The most important property of the waterproofing material is the material's water absorption rate. A satisfactory rate is below 4% (most materials are between 1-2%). Also important is the thickness of the material. Most manufactured materials have a uniform thickness making the application even and easy. The manufacturers state that their protective coatings are can be applied smoothly. This smooth, liquid-only appearance provides a monolithic application with no seams and therefore no weaknesses for cracks to form.

The material should also have some degree of flexibility and be able to resist differential movement. This is especially important for waterproofing membranes in structures that may move/settle (i.e. bridges).

Site Considerations

The proper waterproofing system can only be determined after thorough analysis of the site area. This includes looking at the soil characteristics and water tables.

Soil characteristics - Before construction begins, the soil should be tested to observe the water table level, the presence of hydrostatic pressure, and the chemicals found in the soil. The materials selected must be able to perform at the highest possible hydrostatic water pressure in the area as well as not degrade in the presence of the soil's chemical composition. Acids and alkaline in the ground water can weaken the concrete and steel reinforcement bars. Soil compounds such as salt, sulfates, calcium hydroxides, oils, and chemicals from fertilizers can react with the compounds in the cement or corrode the steel bars. The physical properties of the soil should also be tested. For example, clay soils that have a low permeability limit underground hydrostatic pressure.

Water table - The water table level is important because it determines not only the type of waterproofing required but whether waterproofing is required by code. The International Building Code requires that waterproofing be applied on all below-grade structures where the groundwater table is maintained a minimum of six inches below the ground slab. The water table test should be done when the water table is at its maximum.

Image Credit: Indiana Geological Survey 

Applications

As mentioned, waterproofing is a critical step in the construction of any structure. There are many types of waterproofing membranes and their application depends on several factors including the use of the structure and the construction process. Waterproofing is often seen in the building of houses (basements), parking structures, and patios.

Waterproofing can also been seen in specialized applications such as in shower stalls, bathroom floors, mechanical rooms, pools, and planter boxes. Saltwater and marine applications have specific requirements since they must be able to withstand the corrosion from salt, sand, and wave action.

Standards

ASTM C1127 is the standard guide for the use of high solids content, cold liquid-applied eslastomeric waterproofing membrane with an integral wearing surface.

ASTM D3393 is the standard for coated fabric waterproofness.

IEC 60529 shows the degree of protection provided by enclosures (IP Code)

Resources

Waterproof Magazine

Waterproofing Design Guidelines: Execution

Negative- Side Waterproofing is not a Primary Seal (pdf)

Guidelines for Proper Waterproofing Specifications

Henshell, Justin, and C. W. Griffin. Manual of Below-grade Waterproofing Systems. New York: John Wiley & Sons, 2000. Print.

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Delta Membrane Systems | Weifang Hongyuan waterproof Materials Co.